Field
The present invention relates to a method and apparatus for forming a three-dimensional image, and more particularly, to a method and apparatus for forming a three-dimensional image by selectively expanding a thermally expandable sheet.
Background
A thermally expandable sheet (or a thermally foamable sheet) where a thermally expandable layer (or a foamable layer) containing foamable microcapsules expanding due to heating is formed on one surface of a base sheet has been known in the past. When the thermally expandable sheet is irradiated with light including infrared light after an image pattern having a high light absorption property is printed on this thermally expandable sheet, the region of the thermally expandable layer corresponding to the image pattern is selectively heated and expanded. Accordingly, it is possible to form a three-dimensional image, which corresponds to the image pattern, on one surface of the base sheet.
As the technique for forming a three-dimensional image, for example, JP-A-64-28660 discloses a method including forming a print image using black toner or ink having a high light absorption property on the surface of a thermally expandable sheet that corresponds to a thermally expandable layer, or on the back of the thermally expandable sheet that corresponds to a base sheet; and forming a three-dimensional image by heating and expanding (foaming) the microcapsules of the region of the thermally expandable layer corresponding to the print image by irradiating the thermally expandable sheet with light from a halogen lamp or the like so that light is absorbed in the print image and heat is generated.
Further, for example, JP-A-2001-150812 discloses a method including forming a color image or the like on the surface of the thermally expandable sheet that corresponds to a thermally expandable layer; forming a light absorption pattern, which is formed of a grayscale image so as to correspond to the pattern of the color image formed on the surface, on the back of the thermally expandable sheet that corresponds to a base sheet; generating heat corresponding to the grayscale of the light absorption pattern by irradiating the thermally expandable sheet with light from the back of the thermally expandable sheet; and controlling the degree of the expansion of the thermally expandable layer to adjust the bulge height of a three-dimensional image.
According to the method disclosed in JP-A-2001-150812, it is possible to form a three-dimensional image of which an arbitrary portion is controlled to have an arbitrary bulge height (foam height) according to the pattern of the color image or the like that is formed on the surface of the thermally expandable sheet corresponding to the thermally expandable layer.
However, according to the result of the inventor's verification of these methods of forming a three-dimensional image, when the thermally expandable sheet is irradiated with light to form a three-dimensional image, the thermally expandable layer is expanded and bulges, so that the surface of the thermally expandable sheet is stretched. For this reason, it has been found that the display color of the color image or the like formed on the surface of the thermally expandable sheet becomes pale as compared to the initial state or color development becomes non-uniform, so that non-uniformity occurs. The reason for this is as follows: the surface of a bulging portion of the surface of the thermally expandable sheet is also stretched with the expansion of the thermally expandable layer and the area thereof is increased, so that the colored portion of the color image or the like is also stretched. Accordingly, the colored portion becomes pale, the density of the colored portion is reduced, or cracks are formed. As a result, the background color of the thermally expandable sheet, which is a foundation of the color image or the like, is seen or exposed to the outside so as to be visually recognized. For this reason, there is a problem in that it is not possible to form a good three-dimensional image due to the deterioration of the quality of the color image or the like. Meanwhile, the problem in the related art will also be described in detail in the detailed description to be described below.